This invention relates to a force measuring device and, more particularly, to a measuring device having means for compensating for zero deviation and/or span deviation attributable to temperature change.
A force measuring device, such as a weigher, for converting a force into a digital electrical signal and processing the signal for display may provide a non-zero value under a no-load condition or an incorrect value under a loaded condition. The former is referred to as "zero deviation" and the latter is referred to as "span deviation", both causing an error of measurement. Although this error can be removed by adjusting the device prior to use, it often appears again with variation of the surrounding temperature. Compensating for this error by using a temperature sensing element such as a thermistor has not been sufficiently successful. The opened Japanese patent specification No. 58-95220 disclosed a device in which a reference weight having a known weight value is actually weighed and a ratio of the weight value to the indicated value is calculated and stored as a correction coefficient, thereby compensating for the span deviation. However, a number of reference weights must be prepared for obtaining high accuracy, since the correction coefficient varies with the load to be measured. It is uneconomical and troublesome to always keep and use such a number of reference weights.